Is it possible for my ex-employer to request wage/money back for working past my scheduled time?

I got caught stealing time for around 30 hours (co-worker clocking me in since I was running late). Now they are claiming that I stole over 250 hours because I worked on the days I was not scheduled to (but my manager called me in to work those days because my co-worker called out) and I sometimes work past my scheduled time to finish up my duties, so the store can be ready for tomorrow (it's retail and I was working for stock). Some of the managers knew I was staying past closing time doing work and sometimes asked me for help on their own duties which I gladly helped as well. Then I was caught by the higher ups saying I stole over 250 hours because I wasn't scheduled for that many hours. I'm willing to pay back 30 hours but 250 hours is just way too much and I was actually benefiting the company during those hours. Is it possible to fight it back?